Automatic control for air conditioning means



May 23, 1961 P. c. J. GILSON 2,934,913

AUTOMATIC CONTROL F OR AIR CONDITIONING MEANS Filed Nov. 12, 1954 United States Patent Ofiice Patented May 23, 1961 AUTOMATIC CONTROL FOR AIR CONDITIONING MEANS Pierre Charles Jean Gilson, Campagne-lez-Wardrecques par Wardrecques, France Filed Nov. 12, 1954, Ser. No. 468,507

Claims priority, application France Nov. 26, 1953 5 Claims. (Cl. 34-46) The present invention relates to an improved automatic control device for a drying installation.

It is known that in order to dry certain materials such as ceramic material and wood in a satisfactory manner, it is necessary that the rate of drying be regular, that is, that the drying power of the air utilized for this drying be constant. It is recalled that the expression dry ing powerof air relates to the number of grams of water that a kilogram of air can absorb before being saturated with steam. As the drying air is taken from an exterior source (surrounding air) having variable characteristics, in particular as concerns its humidity and temperature, the drying power of the air was heretofore held constant by maintaining its temperature and humidity constant, these being the two factors affecting this drying power. As it is industrially difficult to diminish the humidity of the air at an acceptable cost price, the maximum value observed in the region where the drying was effected was adopted for the constant value for this humidity. As a consequence a low drying power was obtained. Furthermore, when the humidity fell below this maximum value, it was necessary to spray water into the drying air to return it to this value, which was not only illogical but uneconomical.

The invention has for its object to remedy this situation and provides an improved method of drying. This method comprises heating the drying air obtained from an exterior source and automatically regulating this heating in accordance with the degree of humidity of the air thus heated so as to impart to the air a constant drying power while operating at variable temperature and humidity.

Thus, according to the invention neither the temperature nor the humidity is maintained constant but the first is regulated as a function of the second.

A further object of the invention is to provide an automatic control device for this purpose. This device comprises an element responsive to the humidity of the air and an element responsive to the temperature, each of these elements being inserted in an electric circuit to which it transmits its indications, and these two electric circuits being coupled and reacting on one another giving an electric indication dependent on the drying power of the air, the latter being dependent on the humidity and the temperature, and electro-mechanical means which is controlled by this electric indication and acts on the heat ing device.

As the element responsive to humidity, a wet-bulb thermometer and in particular a mercury thermometer may be utilized.

As the element responsive to temperature, a dry-bulb thermometer such as in particular a mercury thermometer may be utilized.

According to the nature of the two responsive elements, the coupling of the two electric circuits in which they are inserted may be realized in difierent ways; an example of such a coupling will be given hereinunder.

-A further object of the invention is to provide a drying installation for carrying out the above-mentioned method and comprising the application of the above! mentioned control device. This installation comprises a heating device connected to an exterior source of air, a drier connected to this heating device by a pipe in which the elements responsive to humidity and temperature of the control device are disposed, the electro-mechanical means of the control device controlling the heating device.

Further features and advantages of the invention will appear from the ensuing description with reference to the accompanying drawing given merely by way of example and in which:

Fig. 1 is a chart showing the drying power of the air as a function of the temperatures read off a web-bulb thermometer and a dry-bulb thermometer in contact therewith;

Fig. 2 is a diagrammatic view of an installation embodying the invention, and

Fig. 3 is a diagrammatic view of one embodiment of the control device of the invention.

As has been mentioned above, the method of the invention comprises heating the air for the drier and regulating this heating in accordance with the humidity content of the air thus heated so as to impart to this air a constant drying power.

In order that a better understanding be had of the invention, there will first be described an installation for carrying out this method, such an installation being diagrammatically illustrated in Fig. 2.

The installation comprises an air heating device 1 which receives air from the exterior through a pipe 2 furnished with a fan 3. A suitable heating means is provided in the air heater. This may be, for example, a steam coil provided with an inlet pipe 4, including an electrically-operated valve 5, and a drainage pipe 6 furnished with a valve 7. The air heater 1 is connected, through a pipe 8, to a drier'9, such as a tunnel dryer in which the material to be dried is disposed, this material being for example ceramic or woodpieces. The water-saturated air issues from the drier through an exhaust flue 10.

According to the invention a control device R responsive to humidity and temperature is disposed in the pipe 8 where it is subjected to the heat of the hot air circulating therein and controls the heating of the air heater 1 in such manner as to impart to the air sent to the drier a constant drying power. To this end, the valve 5 is connected to the terminals of an electric source 11 by way of a circuit 12. which is opened and closed in the manner described hereinunder by the control device R.

Before examining in detail the construction and operation of this device, some elementary details relating to the humid or wet temperatures (Th) and dry temperatures (T d) will be given. It will be recalled firstly that a wet-bulb thermometer is a thermometer whose bulb is surrounded by a water-saturated gauze.

It is known that numerical tables give humidity relative to air (the percentage of water vapour contained in the air relative to the water vapour that water-saturated air contains) as a function of the difference, TdTh, of the indications of a dryor wet-bulb thermometer. Further, other tables give the quantity of water, Q, in g. per kg. of air that saturated air contains at various temperatures. The drying power =D.P. of the air according to the aforementioned definition is therefore In this equation Q is a function of Td and H is a function of Td-T h. Calculation and experiments demonstrates that in plotting Td and Th as co-ordinates, the points corresponding to constant D.P. lie along substantially straight lines, as shown in Fig. 1. In this figure Td are plotted as abscissae and Th as ordinates in degrees centigrade and a group of curves corresponding to increasing D.P. are drawn in (D.P.:S, 10, 15, 20, etc.). I

The control device R shown by way of example in Fig. 3 will now be described.

1 This device comprises an element responsive to humidity H and which includes a mercury thermometer whose bulb 13 is surrounded by a water-saturated gauze 14, and an element responsive to temperature T constituted by a mercury thermometer. The bulb 13 of the thermometer H and the bulb 13a of the thermometer T are arranged to extend into the pipe 8 in order to be exposed to the conditions of humidity and temperature prevailing therein. Any suitable device (not shown) is also provided for maintaining the gauze 14 saturated with water.

The thermometers H and T are inserted in an electric circuit. To this end an electric source S has one of its terminals connected respectively at A and B to the bulbs 13 and 13 whereas its other terminal is connected by a conductor 15 to the point C. Two wires 16 and 17 forming part of the circuit of the element H and the circuit of the element T respectively are connected to this point C. How each of these circuits is closed will now be examined.

Welded in the glass of the thermometer H are electric contacts which are equispaced along the column of the thermometer, for example every third degree. Only four or these contacts, h h k and I2 are shown in Fig. 3.

Each of these contacts is connected to the end of a coil e e e e respectively, the other end of which is connected to the conductor 16. Each of these coils controls a relay, r r r r and each relay comprises two movable contacts which it actuates simultaneously: a first contact, c 0 and 0 which is closed onto the conductor 16 at the left of the point of connection of the corresponding coil when the relay is not excited, and a second contact, d d d d connected to the conductor 17 and co-operating with a fixed contact f f f f respectively.

The contacts of each pair at, f (F, F, etc., are separated when the corresponding relays are not excited but allow through the current in the opposite case. Each of the fixed contacts, f f f is connected to one of the contacts of a series of contacts t t t t welded into the glass of the thermometer T and equispaced along the column, for example every third degree.

In series in the conductor 17 is a coil 18 of a relay 19 provided with a contact 20 which closes or opens the circuit 12 leading to the electric valve controlling the heating means of the air heater 1. The whole of the device R may be housed in a case 21 from which only the bulbs 13 and 13 of the thermometers H and T protrude.

To aid the description of the operation of the control device R, it will be first examined how the following are coupled: the contacts h and t h and t etc. the Wetand dry-bulb thermometers (through the medium of the relays r r etc.) and the contacts d and F, d and f etc. It will be assumed that an air drying power of 20 is desired to be maintained. It will be seen on the curve D.P.:ZO in Fig. 1 that a humid temperature (Th) of 20 C. corresponds to a dry temperature (Td) of 31.6 (point M). The following are also to be seen:

Thus the contacts h 11?, W, k are chosen opposite the divisions 20, 21, 22 and 23 of the wet-bulb thermometer .4 H, and the contacts t t t t opposite the divisions 31 /3; 32 /3, 33 and 33%, these divisions being nearest those to be observed for the corresponding theoretical Td. This difference in respect of the theoretical values introduces only a relatively small error in the drying power. Indeed, Fig. 1 shows that at the above-mentioned humid temperatures an increase of 1 of the drybulb thermometer brings about a change in the drying power from 20 to 22 namely an increase of 10%. As the maximum discrepancy in respect of the theoretical Ta is /3, the D.P. is regulated to Within about i3%, which is sufiicient. If further precision is desired it is merely necessary to arrange that the contacts on the thermometers H and T be closer together, for example separated by A".

The device operates in the following manner: When the temperature of the wet-bulb thermometer H is such that the column of mercury attains the contact h current is established in passing through the contacts 0 c and returns to the battery S through the conductors 16 and 15. The 'coil e of the relay r is excited and the relay r opens the contact 0 which cuts off the current in the coil e and in all coils situated on the left side as seen in Fig. 3. On the other hand, as the contacts W, h, etc. are open owing to the fact that the column of mercury has not yet arrived there, the coils on the right side e e etc. do not receive the current and the contacts c 0 etc. are closed, which permits feeding the coil as with current. Thus each time that the column of mercury establishes a new contact on the thermometer H, the current is cut off in the coils on the left side and there is only one coil supplied and a single relay excited, in this case the relay r This relay r opens the contact c and simultaneously closes the contact d onto the contact F. If the column of mercury of the thermometer T then attained the corresponding contact t the current from the battery S is able to pass through the thermometer T, contacts F, a of the conductor 17, the coil 18 and return to the battery S. As the coil 18 is thus fed with current, it raises the relay 19 and opens the contact 20, so opening the circuit 12, which causes the electric valve 5 to close and the air heater is no longer heated. The temperature then falls and the column of mercury rapidly descends in the thermometer T and opens the contact t so cutting off current to the coil 18. The relay 19 then falls back and the electric valve 5 opens and re-establishes the heating of the air heater 1, and so on. Thus it is seen that the device R regulates the heating of the device 1, in such manner that the temperature of the heated air remains around 312 /3 C., the temperature necessary for obtaining a D.P. of 20 in the hygrometric conditions determined'by a corresponding humid temperature of 21 C.

In the operation just described the contacts h and t cause the opening and closing of the valve 5. If, however, the hygrometric condition of the air taken in through the pipe 2 varies, another pair of coupled contacts enter into action. For example, if the humidity diminishes, the humid temperature increases and the contacts h and t3 controlthe operation. In the opposite case, this would be the function of the contacts h and t and so forth. In each case the drying power of the air is constant and equal to 20. If another drying power is required, it is merely necessary to couple the contacts h and t in another way, in accordance with the curves shown in Fig. 1.

Thus, according to the invention, a constant drying power is automatically obtained, which is of great importance in the drying of certain materials, such as ceramic or wood material for which a badly-performed drying operation could result in considerable waste.

Although a specific embodiment of the invention has been described hereinbefore, it is to be understood that many changes and modifications may be made-therein without departing from the spirit of the invention or the scope of the appended claims.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. Air conditioner for supplying heated air having a constant drying power, comprising a heating device, an electro-mechanical regulating means for the heating device, an input pipe for air taken from an exterior source of air having variable temperature and humidity, this pipe being connected to the heating device, an output pipe for heated air connected to the heating device, a wet-bulb mercury thermometer and a dry-bulb mercury thermometer exposed to the heated air in said output pipe, each thermometer comprising a stem on which are equispaced electric contacts adapted to be contacted by the column of mercury, a first electric circuit in which is inserted the wet-bulb thermometer and a second electric circuit in which is inserted the drybulb thermometer, a source of current for each of the electric circuits, which are established respectively across the column of mercury of each thermometer, relays each of which couples a contact of the wet-bulb thermometer with a contact of the dry-bulb thermometer, whereby the humid and dry temperatures corresponding respectively to these two contacts determine a drying power of the heated air which is identical for all coupled contacts, said electro-mechanical regulating means being controlled by any one of these relays when the column of mercury in the two thermometers attained coupled contacts.

2. Air conditioner for supplying heated air having a constant drying power, comprising a heating device, an electro-mechanical regulating means for the heating device, an input pipe for air taken from an exterior source of air having variable temperature and humidity, this pipe being connected to the heating device, an output pipe for heated air connected to the heating device, a mercury wet-bulb thermometer, this thermometer including a bulb and a stem, a first source of current of which one of the terminals is connected to said bulb, the latter being exposed to the heated air in said output pipe, a series of electric contacts equispaced along the stern of the thermometer and adapted to be contacted by the column of mercury, each of these contacts being connected through the medium of a coil to a first common conductor connected to the other terminal of said first source of current, a series of relays each one of which is controlled by one of said coils and comprises two movable contacts the first of which is disposed on said common conductor and is adapted to open when the mercury has attained the contact of the stem corresponding to its relay, thereby cutting ofi the current in all the coils connected to the contacts of the stem disposed in line with inferior divisions of the stern, a drybulb mercury thermometer comprising a bulb and a stem, a second source of current one of the terminals of which is connected to said bulb, the latter being exposed to the heated air in said output pipe, a series of second electric contacts equispaced along the stem of said dry-bulb thermometer and adapted to be contacted by the column of mercury, a series of fixed contacts each one of which is connected to one of said second electric contacts and each one of which is adapted to be contacted by the second movable contact of one of said relays when it is excited, the first electric contacts and the second electric contacts being thus coupled in pairs, and the humid and dry temperatures corresponding to each pair determining a drying power of the heated air which is identical for all pairs, these second movable contacts being connected to a second common conductor connected to the other terminal of said second source of current, and a relay mounted in series in said second common conductor, said electromechanical regulating means being controlled by said last-mentioned relay.

3. Air conditioner for supplying heated air having a constant drying power, comprising a heating device, electro-mechanical regulating means for the heating device, an input pipe for air taken from an exterior source of air having variable temperature and humidity, this pipe being connected to the heating device, an output pipe for heated air connected to the heating device, a housing fixed to said output pipe, a wet-bulb mercury thermometer and a dry-bulb mercury thermometer, each of these thermometers comprising a bulb extending from the housing and exposed to the heated air in said output pipe and a stem provided with electric contacts which are equispaced and are adapted to be contacted by the column of mercury, a source of current, two electric circuits connected in parallel with the terminals of this source of'current, each of these electric circuits comprising a first conductor starting from one of the terminals of the source of current and connected to the bulb of one of the thermometers and 'a second conductor leading to the other terminal of the source of current and with which are connected in parallel the electric contacts of the stem of the same thermometer, the first electric circuit being connected to the wet-bulb thermometer and the second electric circuit to the dry-bulb thermometer, coils each one of which is connected in series with each connection connecting the electric contacts of the stem of the wet-bulb thermometer to the second conductor of the first electric circuit, a series of relays each one of which is controlled by one of said coils and comprises two movable contacts the first of which is disposed on said second conductor of the first electric circuit and is adapted to open when the mercury has attained the contact of the stern of the wet-bulb thermometer corresponding to its relay, thereby cutting off the current in all the coils connected to the contacts of the stem which are disposed opposite the inferior divisions of the stem, each of the second movable contacts of the relays being connected in series with each connection connecting the electric contacts of the stem of the dry-bulb thermometer to the second conductor of the second electric circuit and adapted to open when the corresponding relay is excited, each of the contacts of the stem of the wet-bulb thermometer being thus coupled to a contact of the stem of the dry-bulb thermometer and each pair of said coupled contacts determining a drying power of the heated air which is identical for all the pairs of coupled contacts, and a relay connected in series with said second conductor of the second electric circuit, said electro-mechanical regulating means being controlled by said last-mentioned relay.

4. In a drying installation comprising a drier, an air conditioner for supplying heated air having a constant drying power to said drier, said air conditioner comprising a heating device, regulating means for the heating device, an input pipe for air taken from an exterior source of air having variable temperature and humidity, this pipe being connected to the heating device, an output pipe for heated air connected to the heating device and adapted to supply heated air to said drier, a housing fixed to said output pipe, a wet-bulb mercury thermometer and a dry-bulb mercury thermometer, each of these thermometers comprising a bulb protruding from the housing and extending into said heated air output pipe and a stem provided with electric contacts which are equispaced and adapted to be contacted by the column of mercury, a source of current, two electric circuits connected in parallel with the terminals of this source of current, each of these electric circuits comprising a first conductor starting from one of the terminals of the source of current and connected to the bulb of one of the thermometers and a second conductor leading to the other terminal of the source of current and with which are connected in parallel the electric contacts of the stem of the same thermometer, the first electric circuit being connected to the wet-bulb thermometer and the second electric circuit to' the dry-bulb thermometer, coils each one of which is connected in series with each connection connecting the electric contacts of the stem of the wetbulb thermometer to the second conductor of the first electric circuit, a series of relays each one of which is controlled by one of said coils and comprises two movable contacts the first of which is connected to said second conductor of the first electric circuit and is adapted to open when the mercury has attained the contact of the stem of the wet-bulb thermometer corresponding to its relay, thereby cutting off the current in all the coils connected to contacts of the stem which are disposed opposite the inferior divisions of the stem, each of the second movable contacts of the relays being connected in series with each connection connecting the electric contacts of the stem of the dry-bulb thermometer to the second conductor of the second electric circuit and adapted to open when the corresponding relay is excited, each of the contacts of the stem of the wet-bulb thermometer being thus coupled to a contact of the stem of the dry-bulb thermometer and each pair of said coupled contacts determining a drying power of th h fltfifl ir which is identical for all the pairs, a relay connected in series with said second conductor of the second electric circuit, said electro-mechanical regulating means being controlled by said last-mentioned relay.

5. The structure as claimed in claim 4, wherein said electro-mechanical means is an electric valve inserted in an electric circuit the opening and closing of which 10 are controlled by said last-mentioned relay.

References Cited in the file of this patent UNITED STATES PATENTS 15 2,050,254 Barnsteiner -7.-- Aug. 11, 1936 2,201,389 De Give May 21, 1940 2,519,475 Kennedy et a1. Aug. 22, 1950 2,643,464 Hadady June 30, 1953 

